Office for Nuclear Regulation

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Wylfa - 2011 periodic shutdown - consent to start up Reactor 1 following a periodic shutdown

Licence Instrument 549

Permission requested

Magnox Ltd, the site licence company (the Licensee) that operates and maintains Wylfa Power Station, has requested ONR consent to restart Reactor 1 at the end of its 2011 periodic shutdown in accordance with Licence Condition 30(3) of Nuclear Site Licence 58A.


Wylfa Power Station consists of two Magnox reactors. During operation the reactors are cooled by high-pressure gas, which is circulated through the reactors and then fed to boilers where the heat boils water, turning it into steam, to drive turbines which then generate electricity.

To continue to operate safely and reliably reactors require examination, inspection, maintenance and testing. Continuous improvement also requires plant upgrades to be implemented. Whilst some of these activities can take place when a reactor is generating electricity, many of them require a reactor to be shut down and at relatively low temperatures. To enable such activities each reactor at Wylfa undergoes a periodic shut down every two years. Following a periodic shutdown the reactor cannot start-up without the permission of ONR.

The current shutdown for Reactor 1 at Wylfa commenced on 17 August 2011.

Assessment and inspection work carried out by ONR in consideration of this request

ONR has undertaken a number of inspections and assessments in relation to this request. The most significant are as follows:

Matters arising from ONR's work

There are no significant findings from the periodic shutdown that would prevent the reactor restarting.


The ONR programme of inspections and assessments gives sufficient confidence to issue Consent to start-up the reactor at Wylfa following its periodic shutdown.


Consent to start up the reactor should be given by issuing Licence Instrument Number 549 to the licensee.